THE RELATIONSHIP BETWEEN THE NITRATE CONCENTRATION AND HYDROLOGY OF ASMALL CHALK SPRING - ISRAEL

Discharge from a spring draining a small, perched. Cretaceous chalk aq uifer in the Upper Galilee, Israel, was monitored over a period of two years. The water has elevated nitrate concentrations, with N-15/N-14 and chemical data suggesting that it is a mixture of low-nitrate and h igh-nitrate end-members; the Latter derived from the sewage of a centu ries-old village served by septic tanks. Hydrograph data allowed disti nction between fissure flow during the period of winter rainfall, and matrix drainage during the dry summer months. These different flow typ es, however, did not have markedly different nitrate concentrations: a 50-fold increase in spring discharge due to fissure flow, compared wi th matrix drainage, was reflected in only a 35% decrease in nitrate co ncentrations, The relatively high nitrate concentrations in the fissur e waters suggests that they have had close contact with, and are possi bly displaced from the matrix. This should help to accelerate the decl ine in the spring's nitrate concentrations following the recent comple tion of the village's central sewage drainage system. (C) 1998 Elsevie r Science B.V.